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Commit a5ccfee0 authored by Anton Blanchard's avatar Anton Blanchard Committed by Benjamin Herrenschmidt
Browse files

powerpc: Fix RCU idle and hcall tracing 



Tracepoints should not be called inside an rcu_idle_enter/rcu_idle_exit
region. Since pSeries calls H_CEDE in the idle loop, we were violating
this rule.

commit a7b152d5 (powerpc: Tell RCU about idle after hcall tracing)
tried to work around it by delaying the rcu_idle_enter until after we
called the hcall tracepoint, but there are a number of issues with it.

The hcall tracepoint trampoline code is called conditionally when the
tracepoint is enabled. If the tracepoint is not enabled we never call
rcu_idle_enter. The idle_uses_rcu check was also done at compile time
which breaks multiplatform builds.

The simple fix is to avoid tracing H_CEDE and rely on other tracepoints
and the hypervisor dispatch trace log to work out if we called H_CEDE.

This fixes a hang during boot on pSeries.

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 7b3480f8

arch/powerpc/kernel/idle.c

+2 −10
Original line number Diff line number Diff line
@@ -50,12 +50,6 @@ static int __init powersave_off(char *arg) 
}

__setup("powersave=off", powersave_off);



#if defined(CONFIG_PPC_PSERIES) && defined(CONFIG_TRACEPOINTS)

static const bool idle_uses_rcu = 1;

#else

static const bool idle_uses_rcu;

#endif



/*

 * The body of the idle task.

 */
@@ -67,7 +61,6 @@ void cpu_idle(void) 
	set_thread_flag(TIF_POLLING_NRFLAG);

	while (1) {

		tick_nohz_idle_enter();

		if (!idle_uses_rcu)

		rcu_idle_enter();



		while (!need_resched() && !cpu_should_die()) {
@@ -106,7 +99,6 @@ void cpu_idle(void) 


		HMT_medium();

		ppc64_runlatch_on();

		if (!idle_uses_rcu)

		rcu_idle_exit();

		tick_nohz_idle_exit();

		preempt_enable_no_resched();

arch/powerpc/platforms/pseries/lpar.c

+10 −4
Original line number Diff line number Diff line
@@ -546,6 +546,13 @@ void __trace_hcall_entry(unsigned long opcode, unsigned long *args) 
	unsigned long flags;

	unsigned int *depth;



	/*

	 * We cannot call tracepoints inside RCU idle regions which

	 * means we must not trace H_CEDE.

	 */

	if (opcode == H_CEDE)

		return;



	local_irq_save(flags);



	depth = &__get_cpu_var(hcall_trace_depth);
@@ -556,8 +563,6 @@ void __trace_hcall_entry(unsigned long opcode, unsigned long *args) 
	(*depth)++;

	preempt_disable();

	trace_hcall_entry(opcode, args);

	if (opcode == H_CEDE)

		rcu_idle_enter();

	(*depth)--;



out:
@@ -570,6 +575,9 @@ void __trace_hcall_exit(long opcode, unsigned long retval, 
	unsigned long flags;

	unsigned int *depth;



	if (opcode == H_CEDE)

		return;



	local_irq_save(flags);



	depth = &__get_cpu_var(hcall_trace_depth);
@@ -578,8 +586,6 @@ void __trace_hcall_exit(long opcode, unsigned long retval, 
		goto out;



	(*depth)++;

	if (opcode == H_CEDE)

		rcu_idle_exit();

	trace_hcall_exit(opcode, retval, retbuf);

	preempt_enable();

	(*depth)--;